This invention generally relates to cardiac arrhythmia monitoring. In particular, the present invention pertains to a syncope monitor. Even more particularly, the present invention pertains to a syncope monitoring device that subcutaneously measures and records information regarding syncope.
Nearly half of all Americans will have at least one episode of syncope (sudden transient loss of consciousness) in their lives. It has been estimated that as many as one million people are evaluated and treated for syncope each year in the United States at a cost to the health care industry of more than one billion dollars. More than 100,000 patients per year report to their doctors repeated episodes of syncope. Depending on the cause of the syncope, the prognosis varies from excellent to poor. There are many causes of syncope, but more than half of the episodes have a recognizable cardiovascular cause. When structural heart disease is present, syncope often signals a mechanical or electrical cardiac cause. When structural heart disease is absent, a disorder of cardiovascular reflexes is the most likely cause of syncope. Syncope can be associated with bodily injury due to falls or other accidents. Additionally, individuals who experience syncope may have a serious underlying cardiac condition and may run the risk of increased mortality or morbidity if the condition is left undiagnosed.
External ambulatory monitors that record an electrocardiography (ECG) continuously or during predetermined symptoms are often prescribed. Patients may wear such devices, such as halter monitors, for one day to several months. However, for patients whose symptoms occur infrequently, the monitoring period may not be long enough to capture a diagnostic ECG. Additionally, patient compliance with long term use of such monitors is problematic and can limit or hinder normal activities such as swimming, bathing and even dressing. Another deficiency with external monitoring devices is that many patients being monitored for syncope will suffer fibrillation and die while being monitored.
Approximately 400,000 Americans succumb to ventricular fibrillation each year. It is known that ventricular fibrillation, a usually fatal heart arrhythmia, can only be terminated by the application of an electrical shock delivered to the heart. This shock is delivered through electrodes applied to the chest and connected to an external defibrillator or through electrodes implanted within the body and connected to an implantable cardioverter defibrillator (ICD). Often times paramedics cannot respond rapidly enough with their external defibrillators to restore life. New methods of dealing with this problem including less expensive external defibrillators (and thus more readily available) and smaller implantable defibrillators are being introduced.
A typical ICD includes an electrical pulse generator and an arrhythmia detection circuit coupled to the heart by a series of two or more electrodes implanted in the body. A power supply, and one or more charge storage capacitors are used for delivering defibrillation shocks in the form of electrical current pulses to the heart. These devices try to restore normal rhythm to a fibrillating heart. While ICDs work well at restoring normal function, the ICD is expensive and large in size and not practical for a truly prophylactic device. ICDs are designed to furnish hundreds of high voltage defibrillation shocks over a period of years.
Various researchers have tried to reduce the energy thresholds required for defibrillation. For example, Kirchoff experimented with local pacing during fibrillation in dog hearts (c. 1993; 88: 736-749). Kirchoff used 0.5 mm diameter electrodes and pacing stimuli. As expected, small areas around the heart were captured but no pumping action was expected or detected. Similar results have been obtained in the ventricle by KenKnight (Journal of the American College of Cardiology, 1994; 283A). A number of researchers have tried multiple pulse defibrillation without success in reducing the energy thresholds. Schuder (Cardiovascular Research; 1970, 4, 497-501), Kugelberg (Medical and Biological Engineering; 1968, 6, 167-169), Resnekov (Cardiovascular Research; 1968, 2, 261-264), and Geddes (Journal of Applied Physiology; 1973, 34, 8-11). More recently, Sweeney in U.S. Pat. No. 4,996,984 experimented with multiple (primarily dual) shocks timed based on calculations from the fibrillation rate. None of the above approaches significantly reduced voltages needed to effectively defibrillate a heart.
As can be appreciated from the above, there is an acute need for a improved means of monitoring syncope. The known devices are bulky, uncomfortable, and may miss the desired event.
As stated above, there is an acute need for an improved syncope monitoring device. In particular, there is a need for a small implantable device capable of monitoring syncope and maintaining a minimal cardiac output in the event of fibrillation is needed.
The present invention comprises a method and an apparatus for monitoring syncope. In one embodiment of the present invention, the syncope monitor includes electrical cardiac output forcing (ECOF) back up. The present invention is an implantable device for recording the electrical activity within a human heart. The device of the present invention includes ECOF back up. The device includes a power supply for operating the device and for providing the necessary output forcing signals. A monitoring or detection device is connected to the power supply. The device can monitor blood pressure (BP), and record and store blood pressure readings. Electrodes electrically connect the power supply and the detection device to a patient""s heart. A memory device is also provided which is connected to the detection device for recording electrical activity data of the patient""s heart. In a preferred embodiment of the present invention, the memory device is comprised of a short term loop buffer for continuously recording the electrical data from the patient""s heart and a long term storage buffer. The short term loop buffer may be of a desired size, for example, capable of storing from 1-30 minutes of data before overwriting occurs. Upon the occurrence of a predetermined event, for example, a bout of syncope, the data in the short term loop buffer is transferred to the long term storage buffer. An output control circuit is also provided which is connected to the detection device and to the power supply and to the electrodes. Upon the occurrence of a second predetermined event, such as fibrillation of the heart, the output control circuit causes the delivery of an electrical cardiac output forcing signal to the patient""s heart.